European Patent Application No. 0,241,223 discloses toner compositions which are produced by monomer polymerization in the presence of polyethyleneimine as a dispersant. Also Japanese Patent Application Nos. J63199365-A, J59226357A, J59220151, and J57182753 teach toner compositions containing a binder, a charge control agent, a colorant and polyethyleneimine. In such prior art toner compositions, the polyethyleneimine is a high molecular weight, branched, amorphous material which is typically water soluble.
Commercial polyethyleneimines can be characterized as possessing a highly branched structure containing primary, secondary, and tertiary amine groups. This structure leads to an amorphous material with such a significant hydrophilic character that these commercial materials are provided as aqueous solutions. Addition of this type of polyethyleneimine in toners results in depressed environmental keeping properties and developer RH sensitivity. The utilization of a linear crystalline polyethyleneimines composed of only secondary amine groups, as described by E. J. Goethals and K. J. Weyts, Polymer Bulletin, Volume 19, 13-19 (1988), and also by T. Saegusa et. al., Macromolecules, Volume 15, 707 (1982), circumvents these undesirable effects while still providing an improvement in toner adhesion. This is accomplished by the polyethleneimine being a separate crystalline phase in the toner particle that does not adversely affect the toner keep properties or developer RH sensitivity, yet when melted in the fusing process contributes in a positive manner to the toner-paper adhesion properties.
In toner compositions wherein toner particles are blended with magnetic carrier particles, particularly coated magnetic carrier particles, it is desirable to reduce flakes, hollow character defects, and carrier particle aging. Substantial improvement in such properties can be achieved by including in the polymeric toner particles a fatty acid amine derivative (preferably a quaternary amine compound) as a charge control agent and a lubricant such as polydimethylsiloxane. Unfortunately, such agents seriously interfere with the ability of the toner particles to adhere strongly to copy paper upon heat fusion. Well adhered, heat fused images are necessary for commercially acceptable quality in electrophotographically-made document copies.
In order to achieve commercially useful toner powders containing such charge control agents and lubricants, it is desirable to include in the toner powder composition at least one agent which minimizes the poor adhesion capacity. Previous efforts to find such an additive, however, have generally failed.
Nothing in the prior art teaches or suggests the use of a low molecular weight, crystalline, particulate polyethyleneimine as an adhesion enhancer for overcoming the adhesion reducing effects of the combination of a fatty acid amine charge control agent and a polydimethylsiloxane lubricant in toner compositions.